On social networks and collaborative recommendation

Social network systems, like last.fm, play a significant role in Web 2.0, containing large amounts of multimedia-enriched data that are enhanced both by explicit user-provided annotations and implicit aggregated feedback describing the personal preferences of each user. It is also a common tendency for these systems to encourage the creation of virtual networks among their users by allowing them to establish bonds of friendship and thus provide a novel and direct medium for the exchange of data. We investigate the role of these additional relationships in developing a track recommendation system. Taking into account both the social annotation and friendships inherent in the social graph established among users, items and tags, we created a collaborative recommendation system that effectively adapts to the personal information needs of each user. We adopt the generic framework of Random Walk with Restarts in order to provide with a more natural and efficient way to represent social networks. In this work we collected a representative enough portion of the music social network last.fm, capturing explicitly expressed bonds of friendship of the user as well as social tags. We performed a series of comparison experiments between the Random Walk with Restarts model and a user-based collaborative filtering method using the Pearson Correlation similarity. The results show that the graph model system benefits from the additional information embedded in social knowledge. In addition, the graph model outperforms the standard collaborative filtering method.</p

Dust-scattering rings of GRB 221009A as seen by the Neil Gehrels Swift satellite: can we count them all?

We present the first results for the dust-scattering rings of GRB 221009A, coined as the GRB of the century, as observed by the Neil Gehrels Swift satellite. We perform analysis of both time resolved observations and stacked data. The former approach enable us to study the expansion of the most prominent rings, associate their origin with the prompt X-ray emission of the GRB and determine the location of the dust layers. The stacked radial profiles increase the signal-to-noise ratio of the data and allows detection of fainter and overlapping peaks in the angular profile. We find a total of 16 dust concentrations (with hints of even more) that span about 15 kpc in depth and could be responsible for the highly structured X-ray angular profiles. By comparing the relative scattered fluxes of the five most prominent rings we show that the layer with the largest amount of dust is located at about 0.44 kpc away from us. We finally compare the location of the dust layers with results from experiments that study the 3D structure of our Galaxy via extinction or CO radio observations, and highlight the complementarity of dust X-ray tomography to these approaches.Comment: 12 pages, 10 figures, accepted for publication in MNRAS. New version contains updated tables/figures after correction of a numerical erro

Primary Malignant Fibrous Histiocytoma of the Lung: A Case Report

Primary malignant fibrous histiocytoma (MFH) of the lung is extremely rare although it is among the most common soft tissue sarcomas in adults. Surgery is the primary mode of therapy, with high rates of local and distant recurrence, while radiation therapy appears to be a very useful adjunct, decreasing local relapse. We report a case of primary malignant fibrous histiocytoma of the lung. Fourteen years after surgical resection, the patient is still alive although with multiple metastatic lesions throughout his body

Wind Load Transfer Mechanisms on a Low Wood Building Using Full-scale Data

The wind-induced response of low-rise wood buildings has been evaluated by monitoring a specially instrumented test building exposed to real wind action. The field facilities included a state-of-the-art data acquisition system which collected wind, pressure and force data. In addition to the field monitoring, a 1:200 scaled model of the test building was tested in the wind tunnel and the envelope wind pressures were estimated for various terrain exposures. The wind-induced pressures obtained from both the full-scale and wind tunnel experiments were incorporated in the finite element model of the test building and its response was numerically derived. Vast amounts of experimental data were generated during the long-term monitoring of the test building. These data were used to successfully verify the simulation approaches in terms of both wind-induced pressures and structural forces. Some limited discrepancies were observed in the peak pressure coefficients for locations close to the roof ridge and corners. The field acquired force data revealed that the majority of the wind uplift force is supported by the two side walls. Moreover, it was experimentally verified that the wind-induced load was attenuated as it was transferred through the buildings' structural system. This attenuation was estimated to be at least 17%, as far as the total foundation uplift force is concerned, and reached the 28% for certain approaching wind directions

Wind-induced Pressures on Patio Covers

A wind tunnel study has been carried out to assess wind loads on patio covers attached to low-rise buildings. A 1:100 geometric scale building and patio cover model was constructed and tested for open exposure conditions. The patio cover model was instrumented with pressure taps on both top and bottom surfaces, allowing the simultaneous measurement of wind pressure/suction on each side of the patio cover. The effect of building/patio height was considered by testing three different model configurations. Local surface and net wind pressure and force coefficients are presented for each model configuration. Correlation analysis was carried out to demonstrate how wind flow on the top and bottom of the patio cover affects the total wind load. The findings are also compared to the limited design guidelines derived by current building codes. Finally, recommendations for design wind load standards and codes of practice are made

High resolution mapping of Twist to DNA in Drosophila embryos: Efficient functional analysis and evolutionary conservation

Cis-regulatory modules (CRMs) function by binding sequence specific transcription factors, but the relationship between in vivo physical binding and the regulatory capacity of factor-bound DNA elements remains uncertain. We investigate this relationship for the well-studied Twist factor in Drosophila melanogaster embryos by analyzing genome-wide factor occupancy and testing the functional significance of Twist occupied regions and motifs within regions. Twist ChIP-seq data efficiently identified previously studied Twist-dependent CRMs and robustly predicted new CRM activity in transgenesis, with newly identified Twist-occupied regions supporting diverse spatiotemporal patterns (>74% positive, n = 31). Some, but not all, candidate CRMs require Twist for proper expression in the embryo. The Twist motifs most favored in genome ChIP data (in vivo) differed from those most favored by Systematic Evolution of Ligands by EXponential enrichment (SELEX) (in vitro). Furthermore, the majority of ChIP-seq signals could be parsimoniously explained by a CABVTG motif located within 50 bp of the ChIP summit and, of these, CACATG was most prevalent. Mutagenesis experiments demonstrated that different Twist E-box motif types are not fully interchangeable, suggesting that the ChIP-derived consensus (CABVTG) includes sites having distinct regulatory outputs. Further analysis of position, frequency of occurrence, and sequence conservation revealed significant enrichment and conservation of CABVTG E-box motifs near Twist ChIP-seq signal summits, preferential conservation of ±150 bp surrounding Twist occupied summits, and enrichment of GA- and CA-repeat sequences near Twist occupied summits. Our results show that high resolution in vivo occupancy data can be used to drive efficient discovery and dissection of global and local cis-regulatory logic

Application of neural networks to synchro-Compton blazar emission models

Jets from supermassive black holes in the centers of active galaxies are the most powerful persistent sources of electromagnetic radiation in the Universe. To infer the physical conditions in the otherwise out-of-reach regions of extragalactic jets we usually rely on fitting of their spectral energy distribution (SED). The calculation of radiative models for the jet non-thermal emission usually relies on numerical solvers of coupled partial differential equations. In this work machine learning is used to tackle the problem of high computational complexity in order to significantly reduce the SED model evaluation time, which is needed for SED fitting with Bayesian inference methods. We compute SEDs based on the synchrotron self-Compton model for blazar emission using the radiation code ATHE${\nu}$A, and use them to train Neural Networks exploring whether these can replace the original computational expensive code. We find that a Neural Network with Gated Recurrent Unit neurons can effectively replace the ATHE${\nu}$A leptonic code for this application, while it can be efficiently coupled with MCMC and nested sampling algorithms for fitting purposes. We demonstrate this through an application to simulated data sets and with an application to observational data. We offer this tool in the community through a public repository. We present a proof-of-concept application of neural networks to blazar science. This is the first step in a list of future applications involving hadronic processes and even larger parameter spaces.Comment: 12 pages, submitted, comments are welcome, code will be soon available at https://github.com/tzavellas/blazar_m

Variability of Pennsylvanian-Permian Carbonate Associations and Implications for NW Pangea Palaeogeography, East-Central British Columbia, Canada

Different stages of Pennsylvanian-Permian carbonate sedimentation in east-central British Columbia record a complex history of changing environments influenced by evolving palaeogeography and climate. Newly recognized tectonically controlled features affected the distribution and variability of carbonate associations, providing new interpretations for this portion of the west coast of Pangea. Both a heterozoan (cool water) and photozoan (warm-water) association were identified on either side of a palaeogeographic high here informally termed “Tipinahokan Peninsula”. Cool water carbonates were located outboard, or to the west of this high, an area influenced by upwelling waters. Inboard of this high, a warm, protected sea developed, here termed “Kisosowin Sea”. This configuration and palaeolatitude is similar to that of Baja California, Mexico and the Sea of Cortéz, providing a good modern analog for these deposits where warm water carbonates grow at latitudes otherwise dominated by cool water deposits. The warm sea provided a place for a photozoan association to develop during the Permian when the low latitude NW coast of Pangea was dominated by cool water carbonates

Evaluation of the water resources of the brackish karstic spring of Armyros in Heraklion Crete

164 σ.Η παρούσα διπλωματική εργασία έχει ως θέμα την αξιολόγηση του υδατικού δυναμικού της υφάλμυρης καρστικής πηγής του Αλμυρού ποταμού στο νομό Ηράκλειου στην ΚρήτηThe subject of this diploma thesis is the evaluation of the water resources of the brackish karstic spring of Almyros in Heraklion Crete.Νικόλαος Ι. Σταθόπουλο